A method for direct assessment of tissue-nonspecific alkaline phosphatase (TNAP) inhibitors in blood samples.

Tissue nonspecific alkaline phosphatase (TNAP) is one of four human alkaline phosphatases (AP), a family of exocytic enzymes that catalyze hydrolysis of phospho-monoesters in bone, liver, kidney, and various other tissues. Overexpression of TNAP gives rise to excessive bone and soft tissue mineralization, including blood vessel calcification. Our prior screening campaigns have found several leads against this attractive therapeutic target using in vitro assay with a recombinant enzyme; these compounds were further optimized using medicinal chemistry approaches. To prioritize compounds for their use in animal models, we have designed and developed a biomarker assay for in situ detection of TNAP activity within human and mouse blood samples at physiological pH. This assay is suitable for screening compounds in 1,536-well plates using blood plasma from different mammalian species. The user may choose from two different substrates based on the need for greater assay simplicity or sensitivity.